JPH0653604B2 - Ceramic material articles - Google Patents

Abstract

The invention relates to ceramic articles. It relates to an article made of ceramic material produced by fusing and casting in a mold a composition based on alumina, zirconia, silica and an alkali metal oxide, said article consisting of crystalline corundum and zirconia phases and of a vitreous phase, said zirconia being substantially in monoclinic form from the core to the skin of said article, and having, in at least one of its parts, a thickness lower than or equal to 30 mm and being intended for an application where mechanical strength and/or abrasion resistance are of primary importance, said composition consisting essentially, in % by weight based on the oxides, of: -Al2O3 40-75 -ZrO2 20-55 -SiO2 5-20 -Na2O 0-2.7 -K2O 0.15-4.25 -Fe2O3 + TiO2 + CaO + MgO 0-2, - with the condition that the weight ratio <IMAGE> is between 0.07 and 0.14 inclusive. Application as micronizer disc, pump wear component and antiabrasion slab.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention melts a composition of Al ₂ O—ZrO ₂ —SiO ₂ —K ₂ O system,
It relates to thin ceramic articles with good mechanical strength and wear resistance obtained by casting in moulds.

A refractory material obtained by melting a composition mainly containing alumina, zirconia and silica, which is abbreviated as AZS, and casting it in a mold is well known, and is a structural material for a glass manufacturing furnace in the form of a refractory block. Widely used as. Among others, U.S. Pat.Nos. 2,271,366 and 2,4
38,552, 2,903,373 and French Patent 1,153,4
No. 88 describes such substances. In addition to the main constituents being alumina, zirconia and silica, these patent specifications describe the presence of small amounts of alkali metal oxides which form part of the composition a glassy phase for binding the crystalline phase of the refractory material. Says. Na ₂ O or K ₂ O or mixtures thereof are the ones most commonly described as alkali metal oxides and are listed as synonymous. But,
In industrial practice, Na ₂ O is low cost and Na ₂ O
Is commonly used because its source (sodium carbonate is a common source) is more readily available.

In particular, in addition to pure refractory applications in contact with molten glass, Al ₂ O--ZrO ₂ --SiO ₂ --N ₂ O based melt cast products are advantageous for abrasive resistant applications at room or elevated temperatures. It has become clear that it exhibits characteristics.

In fact, the corundum-zirconia crystal lattice, which can be associated with eutectics, is very hard and very strong. Furthermore,
The bonding by the glassy phase and the absence of open pores, which characterize the melt-cast oxides, provides a product with outstanding bonding strength that is very useful in wear resistant applications.

Also, Al ₂ O--ZrO ₂ --SiO ₂ --Na ₂ O based melt cast products have a wide range of erosion agents other than molten glass, such as dissolved or molten salts, acids or bases (even in concentrated solutions), It has been clarified that it has excellent resistance to corrosion by molten metal and the like.

On an industrial scale, in addition to large refractory blocks, the development of the new types of applications mentioned above has led to alternative resistance to metals (steels-cast irons) or synthetics (plastics) or natural substances (plaster). It has led to the production of thin slabs for wear and corrosion resistant coatings.

Developments in the field of melt processing of oxides make it possible to produce parts of complex or less complex shape by being able to simplify the mold matching and to reduce the joints to a minimum.

In some applications, the wear problem is complicated by external mechanical stress (shock, vibration). In other cases, the function of the article (the member that rotates in the wear or corrosive medium) itself involves these stresses. In one novel application, structural members consisting of melt-cast oxides are selected for their chemical inertness, low thermal conductivity or light weight compared to metals, and are not subject to mechanical stress or heat when applied. Substantially receives mechanical stress.

Surface (or skin) imperfections are less important because large refractory blocks are subject to corrosion, but in thin articles surface (skin) imperfections are related to their geometrical requirements (surface to thickness). It is readily appreciated that it is of decisive importance due to the relative size of the defects) and the stress requirements in use (risk of mechanical failure caused by the abovementioned defects).

From the failure mechanism, the strength of a material can be expressed as: Where 6 _R = Fracture stress (measured, for example, by bending test) K _c = Toughness or critical stress intensity factor at failure Y = Geometric factor (depending on the sample in question) a _c = Corresponding critical defect Length Accordingly, the mechanical strength is as follows: -proportional toughness of a material is proportional to toughness at break, -critical dimension of critical defects depending on manufacturing conditions, perhaps type of article, etc. Inversely proportional to the square root.

The toughness of ceramics is one digit lower than that of metals. This means that if the same mechanical strength is targeted, then the size of the permissible defects in the ceramic will need to be two orders of magnitude smaller than the size of the metal defects (for example, a metal defect size of 1 mm. To 10 μm).

AZS type melt cast ceramics are not exempt from this law. Therefore, reduction of defect size proves to be of primary importance when attempting to manufacture an article that is subject to mechanical stress.

The strength of ceramics is much lower in tension than in compression; this feature makes ceramic articles very sensitive to surface defects. Therefore, ceramic articles must be formed with special care.

Examining the main defects of thin melt cast articles made of AZS, they can be divided into two groups: -shrinked porous type internal defects, -surface crack type internal defects.

From the above considerations, the critical defect would be the latter. This hypothesis is supported by inspection of used melt-cast components that have been mechanically stressed during use indicating that sudden or gradual failure almost always begins with a surface crack.

Therefore, a method aimed at improving the mechanical strength of thin melted and cast articles consists in reducing surface cracking.

Microscopic inspection of surface cracks in thin melted and cast articles of AZS shows that surface cracks are always present in the glass phase joining the entangled portions of the product grains.

When solidifying a product of this kind, the glass phase finally sets to a solid. While the product is able to absorb some stresses and strains while the glass phase is plastic, the risk of cracking becomes very great when the glass phase solidifies.

Thus, it will be readily seen that the nature of the glass phase plays a substantial role in crack initiation in the melt cast product of AZS.

This glass phase is usually about 70% silica (SiO ₂ ), about 25% alumina (Al ₂ O ₃ ), about 5% sodium oxide (Na ₂ O) + traces of other dissolved by weight. It is composed of oxides (ZrO ₂ , CaO, Fe ₂ O ₃ , TiO ₂ ).

In this type of product, the term "trace amount" is usually about
It means less than 0.05% by weight.

The possibility of modifying the glass phase to improve surface cracks by modifying the solidification conditions appears to be relatively limited.

Silica glass in equilibrium with corundum is saturated with alumina and the only variable factor is the alkali metal oxide.

Lowering the proportion of Na ₂ O immediately affects the appearance of mullite, with a whole series of defects (cracks, chipping, etc.).

Although it seems to have a slightly positive effect on the surface cracks of a thin member that increasing the proportion of Na ₂ O, an increase in the proportion of Na ₂ O is very limited (cracking later), also, high temperature properties Have an unfavorable effect on

Applicants have sought to completely or partially replace sodium oxide with other alkali metal oxides. In the periodic table of elements, the alkali metals up to the sixth period are shown in the order of increasing atomic weight as follows. : Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Cesium (Cs) From the next cycle (Francium), all isotopes of the element in question are radioactive, which means that Is obviously a problem.

Among the above-mentioned alkali metals, Li, Na, and K can be industrially obtained in the form of carbonate without serious problems, but Rb and C _s are few and expensive. Nevertheless, for better understanding, we have included one of the expensive elements (Ca) in our research. The following table summarizes the key properties of the four alkali metals studied: The alkali metals mentioned above can be conveniently incorporated into the composition of the oxide to be melted in the form of carbonates. This is the method we have chosen for the study. Emission of CO ₂ gas occurs during melting and the alkali metal is recovered in the glass phase of the solidified product in oxide form (Li ₂ O, Na ₂ O, K ₂ O, Cs ₂ O).

The glass phase of the melt-cast AZS product is a mixture of some polymerized complex anions SiO ₄ ^-4 and AlO ₄ ^{5 -} and simple O ^2- and an alkali metal cation Na called a lattice structure modifier (or destroyer). It seems to be a silicate skeleton structure consisting of ⁺ . Complete or partial replacement of Na ⁺ ions with other alkali metals must be done with the same molar number of ions to maintain the normal glass phase / corundum equilibrium in the absence of mullite. With the same number of moles, the substitution of Na ⁺ ion for K ⁺ ion is K ₂ O / Na ₂ O conversion ratio
Yields 1.52. According to this law, 1% N by mass
a ₂ O must be replaced by 1.52% K ₂ O, on the contrary
The molar equivalent of 1.52% K ₂ O on a mass basis is 1% Na ₂ O. Furthermore, in the electrically fused, cast product of the alumina-zirconia-silica type, the weight ratio of Na ₂ O / SiO ₂ is to maintain a good equilibrium between the two phases, especially in the absence of mullite. Must be maintained between 0.07 and 0.14. This law, if the complete replacement or partial replacement of the Na ₂ O is considered to be a Na ₂ O equivalents by mole conversion ratio K ₂ O / Na ₂ O above, K ₂ O-containing composition The same can be applied as. Therefore, the conditions that must be met are: Attempts to produce thin melt-cast AZS articles made under the conditions described above have produced a variety of different results depending on the nature of the alkali metal oxide used.

The Na ₂ O containing AZS control product systematically showed fine surface cracks. Cracks usually have a depth of 3 for a 10 mm thick member
mm.

The Li ₂ O containing AZS product exhibits network cracks that are more closely spaced than the control product. On the other hand, the crack does not seem too deep. Overall, the average strength of the thin article is about the same as that of the control product.

The Cs ₂ O-containing AZS products are few in number but show severe surface cracking. Here, the average strength of the thin article remains about the same as that of the control product.

Surprisingly, we have found that K ₂ O containing AZS compositions result in thin melt cast articles that are substantially free of surface cracks. The bending mechanical strength of thin articles is significantly improved (50-
140%), it was confirmed by various tests that the quality of the surface layer was particularly sound.

Therefore, the present invention is an article of a ceramic material produced by melting a composition mainly containing alumina, zirconia, silica and an alkali metal oxide and casting the composition into a mold, wherein the article is crystalline corundum and zirconia. Phase and glass phase, the zirconia present from the core to the surface of the article is substantially monoclinic, has a thickness of at least 30 mm or less, and has a mechanical strength and / or abrasion resistance. Is intended for applications where is most important, the composition comprises Al ₂ O ₃ 40-75 ZrO ₂ 20-45 SiO ₂ 5-20 Na ₂ O 0-2.7 K ₂ O 0.1 in wt% based on oxide. 5 to 4.25 Fe ₂ O ₃ + Tio ₂ + CaO + MgO 0 to 0.3, and the weight ratio (Na ₂ O + K ₂ O / 1.52) / SiO ₂
The present invention relates to an article made of a ceramic material characterized by being 0.07 to 0.14.

The total of Fe ₂ O ₃ , TiO ₂ , CaO and MgO must be 0.3 wt% or less. In order to obtain good characteristics, the proportion of Na ₂ O is 0
˜1.20 wt% and the proportion of K ₂ O is preferably 0.25 to ₂ %.

The articles of the present invention are particularly useful in applications where mechanical strength and / or abrasion resistance are paramount. For example, although the articles of the present invention are used as ultrafine mills, wear resistant members of pumps for liquids containing solids, wear resistant coatings, etc., it is understood that this description is not intended to limit the application. I want to be done.

It was felt that if potassium ions play a favorable role during solidification of the surface of the AZS composition, this should also appear in features other than surface cracking.

Therefore, we conducted a detailed study using X-ray diffraction to determine the crystalline phases present from the core to the surface in the solidified product as a thin article.

In the case of the AZS control product containing Na ₂ O, the core crystalline phases of the 8 mm thick article are corundum, monoclinic zirconia and glass phases. A similar crystal phase is observed within about 1 mm of the surface layer. From this place to the surface layer, tetragonal zirconia appears more than monoclinic zirconia.

The same type of crystallization can be achieved with Li ₂ O containing AZS and Cs ₂ O containing AZ
Observed in the melt-cast product in the form of a thin article consisting of S; the K ₂ O containing AZS product is an exceptional morphology. In fact, in the K ₂ O containing AZS product, corundum, monoclinic zirconia and glass phase are observed from the product core to the surface. The prominent diffraction lines of tetragonal zirconia rarely appear, and in many cases appear evenly throughout the thickness of the article.

It is considered that the results of each of these crystal phases show more elastic behavior due to the surface layer of the AZS product containing K ₂ O, and upon cooling, the natural allotropic transition of tetragonal zirconia → monoclinic zirconia to the surface layer. While the tetragonal phase is trapped by the sudden solidification and stiffness of the glass composition of other compositions.

When the K ₂ O containing glass phase is adapted to the zirconia transition,
The glassy phase can withstand various solidification and cooling stresses without undue rigidity and without cracking.

Another aspect consists of the finding that the tetragonal zirconia → monoclinic zirconia transition with increasing volume produces a favorable surface compressive stress to minimize the appearance of cracks.

This hypothesis of superficial compressive stress is supported by thermal destressing tests on thin articles. The flexural mechanical strength of the Na ₂ O containing AZS control product is substantially unchanged (slightly increased) after heating at 1100 ° C. for extended periods of time. On the contrary, the mechanical strength of the K ₂ O-containing AZS product deteriorates significantly after the heat treatment at 1100 ° C. and again becomes similar to the mechanical strength of the normal product. This result can be explained by the presence of compressive stress in the surface layer of the K ₂ O-containing AZS product, which improves bending strength but disappears after heat treatment.

Other unique properties of melt cast K ₂ O containing AZS products were observed in the high temperature transition studies of the products. Na ₂ O-containing A
A small sample of the ZS product was heated to 1600 ° C. for 7 hours and then quenched in cold water. It was observed that the behavior of the glass phase of the two products was quite different in this type of test. In the case of the control product, the amount of glass phase is increased by the dissolution of alumina and zirconia, which changes the analytical value. In the case of K ₂ O-containing products, the amount of glass phase and its analytical value are virtually unchanged.
The unique stability of the glass phase of the K ₂ O containing AZS product is an indication of the specificity of the product and certainly plays an important role in solidifying the product.

The present invention will be further described below with reference to Examples, but it should be understood that the present invention is not limited to the following Examples. In the examples, the amount, that is,%
Is entirely by weight.

Example 1 A powder composition of 49.9% alumina (containing a small amount of Na ₂ O), 47.6% zircon sand and 2.5% potassium carbonate to a Heroult type arc furnace for melting oxides. Introduce. The production was carried out under oxidizing conditions (long arc) as described in French patent A-1,208,577. After melting, the cast product has the following analytical values: Al ₂ O 50.1%, ZrO ₂ 32%, SiO ₂ 16%, K ₂ O 1.
7%, Na ₂ O 0.2%, others <0.3% (within analytical accuracy range).

The molten product was cast in a sand mold in the form of clusters of small slabs. Small slabs measuring 120 × 120 × 8 mm are suitable for examining the mechanical properties of the resulting product. 5 × 120 × 20 × 8mm from small slab
Cut out small platelets, each having two large as-cast surfaces.

For comparison, a control Na ₂ O containing AZS product was cast under similar conditions. The powder composition introduced into the furnace is alumina 50.
7%, zircon sand 47.6% and sodium carbonate 1.7%
Contains. After melting, the cast product has the following analytical values: Al ₂ O ₃ 50.8%, ZrO ₂ 32%, SiO ₂ 16%, Na ₂ O.
1.2%, other <0.3%.

A comparison of the mechanical strength of 120 × 20 × 8 mm test specimens of the two products was first made by the conventional method used by potters and refractory experts: 30 individual products The test piece is broken by three-point bending (axial distance 80 mm) using a press device equipped with a measuring instrument, and the breaking elastic modulus is deduced therefrom. Results are shown as mean intensity and standard deviation.

Three-point bending strength standard deviation AZS-Na ₂ O product 50 MPa 10 MPa AZS-K ₂ O product 120 MPa 15 MPa The excellence of the product according to the invention can be very clearly observed from the average mechanical strength.

More detailed mechanical strength studies can be performed using 4-point bending; in fact, the stress volume in the specimen is large, which increases the probability of finding large size defects.

Variations in the mechanical strength of ceramics are well adapted to Weibull statistical analysis.

This analysis of the results leads to a measurement of the parameter m (Weibull modulus), a characteristic of the variation of the mechanical strength and a characteristic of the size of the critical defects (larger m, smaller variation).

This mechanical strength study can be supplemented by elastic modulus measurements. Two non-destructive dynamic test methods were applied to measure the elastic modulus: ultrasonic and resonant frequency.

This more detailed method gives 30 x 120 x individual products.
It was applied to a 120 × 8 mm test piece. The four-point bending strength was measured at axial intervals of 50 mm and 100 mm, and the load was increased at a speed of 0.3 MPa / sec.

The results obtained are shown in the table below.

The 4-point bending mechanical strength increase of the product according to the invention is less pronounced than the 3-point bending, but is very clear. Weibull statistical analysis confirms that there is little variability in the results.

Modulus of elasticity is associated with defects in ceramic specimens. Measurements using ultrasound are more sensitive to core defects and measurements using resonance frequency are more sensitive to surface defects, especially cracks. The above results show that the K ₂ O-containing AZS product has less surface cracking.

120 × 20 × 8mm similar to that used for mechanical testing
The test body of 1 was cut and the surface was polished to obtain a polished surface suitable for the X-ray diffraction test.

Next, the crystalline phases present at known reference angles listed in the ASTM table were qualitatively measured.

Na ₂ O containing AZS materials showed the presence of the following crystalline phases in the surface region: corundum, tetragonal zirconia and monoclinic zirconia. Under the same conditions, the K ₂ O containing AZS material showed the presence of the following crystalline phases: corundum and monoclinic zirconia. This result indicates that the glass phase mainly composed of K ₂ O can control the transition of tetragonal zirconia-monoclinic zirconia.

In Example 2 above examples were observed main effect of K ₂ O in the case of replacing substantially all of the Na ₂ O to K ₂ O. It was observed that the favorable effect of potassium ions was obtained even when the substitution was partial.

Under the same conditions as in Example 1, a cast product was prepared having the composition analyzed as follows.

The mechanical strength was measured by three-point bending as in the method described in Example 1.

The results are summarized in the table below.

Three-point bending strength Composition 1 50 MPa Composition 2 80 MPa Composition 3 95 MPa Composition 4 105 MPa Composition 5 120 MPa Composition 6 120 MPa Potassium ion cracking and mechanical even when potassium ions are introduced at very low proportions It can be clearly observed that it has a favorable effect on strength.

For a given composition, the optimal proportion of K ₂ O is where most sodium ions are replaced by potassium ions (eg composition 5). An excess of K ₂ O (eg composition 6) does not contribute anything to the mechanical strength in the cold.

120 × 20 × 8 mm specimens of the six test compositions were cut and surface polished as described in Example 1.

An X-ray diffraction test showed the presence of corundum, tetragonal zirconia and monoclinic zirconia in the surface region of Composition 1.

A similar crystalline phase was observed in the surface layer of Composition 2,
The peak of tetragonal zirconia was remarkably small.

In Compositions 3 to 6, the tetragonal zirconia disappeared completely, and the surface crystalline layers were only corundum and monoclinic zirconia.

Example 3 Thin melt cast AZS articles are commonly used in wear resistant applications.

It is interesting to observe whether the surface quality advantages of the K ₂ O-containing composition can be obtained strictly from the standpoint of wear resistance and separately from the aspect of appearance and the point of view of mechanical strength.

120 × 120 × 15 using the Na ₂ O-containing control composition described as composition 1 in the previous example and the composition described in example 1 described as composition 5 in the previous example.
mm and 250 × 250 × 25 mm slabs were cast.

The dimensions of the slabs described above can be used in conventional wear resistant applications, such as coatings in circuits for transporting lime.

Abrasion resistance was evaluated by standard tests. Melt-cast brown corundum (0.4-0.6 mm) is sprayed onto the test product at an angle of incidence of 45 ° at a speed of 60 m / s using a pressure of 2.8 bar. The resistance index is at least 1 kg of abrasive
Calculated from the loss of volume in the sample compared to the control's volume loss based on one spray.

The results of the wear of the 120 × 120 × 15 mm slab are as follows. : The results of the abrasion test on a 250 x 250 x 25 mm slab are as follows: From the above results, the surface quality of the AZS-K ₂ O product is seen to have a significant effect in the wear resistance.

It can be seen that the improvement is more pronounced for thinner articles compared to the control product. However, the improvement is superficial because it is quite fine at 1/3 of the slab thickness.

One of the advantages of Example 4 AZS-Na ₂ O composition, to obtain a complex thin articles is very useful for producing a special set thereof for the wear resistant applications or other applications It is possible to form the composition in a molten state.

The AZS-K ₂ O composition know whether to keep the aforementioned advantages for processing into complex articles while retaining specific advantages concerning the surface quality is important.

It was adopted control composition 1 and AZS-K ₂ O composition 5 in the previous embodiment.

The above composition was melted in a conventional hellort furnace and the product was cast in a sand mold to obtain a special disc-shaped member intended for use in a wet mill with a fine media.
These discs are used for propagating the grinding media in the composition to be ground or dispersed and are therefore stressed in terms of mechanical locality and wear resistance.

The disc manufactured in this example has an outer diameter of 200 mm and an average thickness of 1
A member having a central hole for the hob and an edge hole for passing the charge, having a thickness of 5 mm (having a non-uniform thickness: projections are present).

Comparison of the parts obtained with compositions 1 and 5 shows very similar behavior: similar is obtained under similar conditions, similar susceptibility to unregulated (casting temperature, cooling conditions etc.).
However, the improved surface appearance of the surface layer is due to the composition 5 (AZS
-K ₂ O) is observed systematically in the member obtained.

This finding can be corroborated by an invasion control test that can detect surface defects using the appropriate liquid. Cobweb-like fissures are clearly visible when using composition 1, but very few cracks appear when using composition 5.

Resonant frequency is another means that can be used as a non-destructive control test method for thin articles. In the case of complex parts such as the discs mentioned above, the elastic modulus cannot be deduced from the measurement of the resonance frequency. However, for the same geometry, the low resonance frequency will grade the component due to cracking. The 16 discs produced with composition 1 give an average resonance frequency of 4,250 Hz, whereas the 16 discs produced with composition 5 have an average resonance frequency of 4,870 Hz. The frequency is obtained. Furthermore, 32
If we classify the discs in order of increasing frequency, AZ
It can be seen that 13 discs corresponding to the SK ₂ O composition are excellent.

Also, the excellence of disk castings using the composition according to the invention can be demonstrated by using the abrasion test described in Example 3. Superficial abrasion resistance index of AZS-K ₂ O disc is 175, was 129 in the case of AZS-Na ₂ O composition different.

All the above results clearly show the superiority of the composition according to the invention compared to the melt-cast control product in the form of a thin article containing complex parts.

Example 5 In all the examples described above, the melting of the composition in an electric furnace and the production of a molten AZS bath were carried out according to French patent A-1,208,
It was carried out under the highly oxidative conditions recommended by 577.

Current arc melting processes are now commonly used for this type of composition 9.

The compositions of the above examples were all made using relatively pure raw materials (metallurgical alumina, Australian zircon), and the final product should have MgO + CaO + Fe ₂ O ₃ <0.2%. it can.

Here, the practice of limiting impurities corresponds to current methods of producing refractory materials that are electrically melted.

However, the old method (immersed graphite electrode, US Patent No.
No. 2,903,373, page 2, line 60, yielding a product as described by Sandmeyer).
It is also important to confirm the effect of the alkali metal oxide K ₂ O on the AZS product produced with the composition containing the impurities (MgO, CaO, Fe ₂ O ₃ ) of the electroformed AZS product.

A product with the following chemical analysis values was cast under the above conditions.

Composition 7 Al ₂ O ₃ 48.2% ZrO ₂ 32% SiO ₂ 16% Na ₂ O 0.2% K ₂ O 1.9% MgO 0.7% CaO 0.5% Fe ₂ O ₃ 0.5% This composition contains impurities (MgO, CaO). , Fe ₂ O ₃ ) and the reducing treatment.

Composition 7 was also compared to a reduction treated product containing impurities and containing the usual alkali metal oxide Na ₂ O (AZS product melted and cast by the old method).

Composition 8 Al ₂ O ₃ 49.1% ZrO ₂ 32% SiO ₂ 16% Na ₂ O 1.2% K ₂ O 0% MgO 0.7% CaO 0.5% Fe ₂ O ₃ 0.5% on a 120 × 20 × 8 mm test piece The three-point bending mechanical strength at yields the following results: Three-point bending strength Composition 6 120 MPa Composition 7 90 MPa Composition 8 50 MPa This result indicates that the AZS product according to the old method (composition 8,
It clearly shows that the impurity-containing reduced treatment is comparable to the current standard product (Composition 1) in terms of mechanical strength in the form of thin articles.

The same treatment and the use of the alkali metal oxide K ₂ O containing the same impurities (composition 7) gives a marked improvement and the surface has a relatively crack-free appearance.

However, reduction treatments and impurities cannot achieve the surface quality of thin articles of K ₂ O containing AZS products when treated under oxidizing conditions and in the absence of impurities.

120 × 20 × 8 mm specimens of compositions 7 and 8 were cut and surface polished, then X as described in Example 1.
Tested by line diffraction.

Composition 7 containing K ₂ O showed that only corundum and monoclinic zirconia were present in the surface region.

Composition 8 in the absence of K ₂ O showed the presence of corundum, tetragonal zirconia and monoclinic zirconia in the surface region.

The above-mentioned test piece was obtained by cutting two points along the midline at right angles, and therefore, the crystalline phase in the core region can be measured. X-ray diffraction spectrum shows the presence of K ₂ O
Or all the specimens that were absent showed the presence of monoclinic zirconia and Conradam crystals.

Example 6 The obtained small plaque was analyzed to have the following composition (high corundum content): Al ₂ O ₃ 72.5% + ZrO ₂ 21% + SiO ₂ 5.8%
Example 1 was repeated except that it had the same composition as described above except that + Na ₂ O 0.5% (others <0.2%) and K ₂ O 0.5% were added. The appearance and mechanical strength of the cast article are better in the case of the K ₂ O containing composition.

Claims (5)

[Claims] 1. An article of ceramic material produced by melting a composition mainly comprising alumina, zirconia, silica and an alkali metal oxide and casting it in a mold, having a thickness of 30 mm or less. At least one part, the article is composed of crystalline corundum and a zirconia phase and a glass phase, and the zirconia present from the core of the article to the surface layer is substantially monoclinic and has a mechanical strength and / or
Or intended for applications where wear resistance is of paramount importance, wherein the composition comprises Al ₂ O ₃ 40-75 ZrO ₂ 20-45 SiO ₂ 5-20 Na ₂ O 0-2.7 in weight% based on oxide. K ₂ O 0.15 to 4.25 Fe ₂ O ₃ + TiO ₂ + CaO + MgO 0 to 0.3 substantially, and the weight ratio (Na ₂ O + K ₂ O / 1.52) / SiO ₂ is 0.07 to
An article made of a ceramic material characterized by being 0.14. 2. The content of Na ₂ O is 0 to 1.20% by weight, and K ₂ O
2. The article according to claim 1, wherein the ratio is 0.25 to 2% by weight. 3. The article is a micronizer disc.
The listed article. 4. A component according to claim 1, wherein the article is a wear resistant article of a pump for liquids containing solids. 5. The component is a wear resistant coated slab.
The parts listed.